Optical range finder



H. E. IVES OPTICAL. RANGE FINDER Filed Nov. 25, 1945 2 Sheets-Shet 1FIG. 2

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y' wn I7 5 8 I UWQ 15 :E; as (9- 27 1T- 2a 2 2 I4 30 ATTORNEY I 4/ I I67 I 64' n 70 72 I INVENTOR I H E IVES er 7 J 151M ATTORNEY Dec. 11,1945. H. E.' IVES 2,390,652

7 OPTICAL RANGE FINDER 7 Filed Nov. 25, 1943:

2 Sheets-Sheet 2 Patented Dec. 11, 1945 2,390,652 OPTICAL RANGE FINDERHerbert E. Ives, Montclai Laboratori Telephone York, N. Y.,

r, N. J., assignor to Bell es, Incorporated, New a corporation of NewYork Application November 25, 1943, Serial No. 511,664

12 Claims.

This invention relates to range finders.

An object of the invention is to provide improved means in a rangefinder for determining the proper range setting for an object by causingtwo fusible visual representations of an object field including saidobject to flicker at the same rate and in opposite phase, the propersetting being indicated by the absence of flicker of the object beingranged.

In an example of practice of the invention, shutter means are providedin an overlapping image type of range finder to intermittently andalternately eliminate the respective images from the view of theobserver at afrequency to produce observable flicker in each image ifthe other image were eliminated continuously during observation. In thistype of range finder, optical means produce two images of the sameobject field from separated points of view in the focal planeof a singleocular. The two images are relatively adjustable to eifect coincidencein any part of the image field. In normal operation neither image iseliminated continuously but as one fades out the other fades in so thatthe images of objects which are in exact coincidence do not flicker.Correct setting is indicated when the observed image of the target orobject being ranged ceases to flicker. The target may be oatedanywherewithin the field of view.

In one typical arrangement, the shutter means comprises three sheets oflight polarizing material, one well-known type of such material beingknown as Polaroid. Two of these sheets are placed in the respectivelight beams of the image forming light means or telescopes somewherebetween the object field and the common portion of the light paths.These sheets are so oriented that the light beams forming the respectiveimages are polarlzed at right angles to one another at the plan of theoverlapping images. The third sheet of polarizing material which servesas an analyzer, is located in the common path where the respective beamsare polarized at right angles to each other and arranged to be rotatedin the plane of the sheet about an axis perpendicular to analyzer sheetis rotated, each image fades out and fades in as the polarizing axis ofthis sheet passes from parallelism with the plane of vibration of theimage forming beam through an angle of ninety degrees therewith and backinto parallelism. Since the two image forming beams are polarized atright angles to one another, one image fades out as the other fades in.The speed the sheet and parallel and close to the optical axis of thecommon path. As the of rotation of the analyzer sheet is such as tocause each image to appear to flicker. However, such portions of the twoimages as are in exact coincidence appear as a single image and withoutflicker.

In another typical arrangement, rotating slotted shutters are arrangedto interrupt intermittently the respective light beams of the twotelescopes. The shutters may be placed anywhere in the separated lightpaths, one convenient place being at the respective entrance aperturesof the combining optical means. These shutters are arranged to stop onebeam as the other is unstopped so that one image fades out as the otherfades in at the desired flicker rate to make possible easy adjustmentfor coincidence in any portion of the image field.

The use of flicker to facilitate the proper setting of a range finder isapplicable to all types of range finders which rely upon fusion of theobserved images of the object field whether the observing of such fusionrequires only one or both eyes of the observer. Flicker producing meansmay be used with any type of stereoscopic range finder as well as withcoincidence types of range finders.

This invention will now be described more in detail having reference tothe accompanying drawings.

Fig. 1 is a diagrammatic plan view partially in section of an opticalrange finder according to this invention comprising light polarizingshutters;

Fig. 2 is a partial vertical cross-section of Fig. 1 along the line 2-2looking in the direction of the arrows;

Fig. 3 is a cross-section of Fig. 1 along the line 33;

Fig. 4 is a diagrammatic plan view partially in cross-section of amodified optical range finder according to this invention comprisingslotted rotating disc shutters;

Fig. 5 is a partial vertical cross-section of Fig. 4 along the line 5-5;

Figs. 5A and 5B show the relative angular positions of the shutters ofFig. 5;

Fig. 6 is a cross-section of Fig. 4 along the line The same referencecharacters are used to indicate identical elements of the severalfigures of the drawings.

Referring now to Fig. 1, a generally tubular hollow casing 5 is adaptedto support the optical elements of a coincidence range finder. In such arange finder, two images from separated points of view are formed byoptical means in the focal plane of a single ocular. In the arrangementof Fig. 1, the image from the left-hand point of view is formed byobjective lens 6 utilizing light entering through window I. The axis of,this beam of light is represented by dot-and-dash line 8, the directionof which is changed at a right angle by the optical square 9 and againat a right angle by the internally fully reflecting face it of prism H,such axis passing out of prism Ill and through the semi-reflecting face12 of prism I3 to the focal plane of ocular M. The image from theright-hand point of view is formed by objective lens [5 utilizing lightenter ing through window It. The axis of the beam of light from thewindow It is represented by dot-and-dash line ll, the direction of whichis changed at a right angle by an optical square l8 and again at a rightangle by the semi-re fleeting face i2 of prism I3 to coincide with theleft-hand axis represented by line 8. The objective lenses 6 and [5 areso located as to form images of the object field of equal size in thefocal plane of the ocular M. The ocular It may be of any well-knowntype. By means of prism I9 which is movable along the axis H, asindicated by the double headed arrow 35, the image formed by theobjective lens l5 may be moved transversely in the focal'plane of ocularHi. By means of an adjustable prism in the window I, the image formed byobjective lens 6 may be moved both vertically and transversely to effectan infinity setting, that is, to efiect coincidence or} the twooverlapping images in the focal plane of the ocular M when viewing anobject effectively located at infinity and with the prism is set at itsinfinity position which is toward the middle of the casing 5. use ofprisms such as H; and 29 are well known in the prior art. The window 66is closedby a plane glass plate 2|.

According to this invention, a sheet 22 of Polatold is placed at theentrance face of prism H and another'sheet 23 of the same kind is placedat the entrance face of prism l3. These sheets have their polarizingaxes oriented at right angles to one another so that'the' respectivelight beams forming the two images in focal plane of the ocular Ht arepolarized in planes at right angles to one another. The polarizing axisof a sheet is the line of intersection of the plane of vibration of thepolarized beam with a plane surface of the sheet. As shown in Fig. 3 thepolarizing axis of sheet 22 is horizontal as repres'entedby thedouble-headed arrow 24 and the polarizing axis of sheet 23 is verticalas represented by the double-headed arrow 25. A third sheet 26 ofPolaroid is mounted for rotationin the plane of the sheet about an'aXiswhich is parallel to and may coincide with, the axes 8 and H of theleft-hand and right-hand beams, respec tively, where these two beamstraverse a com: mon path. The location of sheet 26 is near the focalplane of the ocular I l. The sheet 26 is mounted inside a hollowspiralgear 21, which gear is supported for rotation in a ring bearing 28mounted on a pedestal 29 secured to the ofiset portion 3i! of easing 5.The gear 21 is driven by a motor 3! through shaft 32 and spiral pinion33. The motor 3| is mounted onthe lower side member of oiiset portion30, the shaft 32 passing through a light-tight opening in this sidemember. The polarizing axis of sheet 26 in the position shown in Fig. 2is vertical as represented by the double-headed arrow 34. 7

With the polarizing sheet 28 in the position shown in Fig. 2, the imageformed by light enter-'- ing the right-hand window [6 which is polarizedby sheet 23 is visible at maximum brilliance because the polarizing axesof sheets 23 and 26 are parallel, that is, the plane of vibration of thelight which has passed through sheet 23 as it arrives at sheet 26 isparallel to the polarizing axis of sheet 26. As the sheet 26 is rotatedby the motor 3i, it assumes a position such that the polarizing axis ishorizontal and the image formed by light entering the left-hand window Iwhich is polarized by sheet 22 is visible at maximum brilliance sincethe plane of vibration of the light which has passed through sheet 22 asit arrives at sheet 26 is horizontal and therefore parallel to thehorizontal polarizing axis of sheet 26. For the sake of brevity, theimage formed by light entering the right-hand windowifi will be calledthe right-hand image, and the image formed by light entering theleft-hand window I will be called the left-hand image. As the sheetrotates from the position shown in Fig. 2 through ninety-degrees, theright-hand image will fade out as the left-hand image fades in. When theright-hand image is at maximum brilliance, the left-hand image is atminimum brilliance. For each complete revolution oi the sheet 25, eachimage assumes maximum brilliance two. times and brilliance two times,Good results have been obtained with the sheet 26 rotating at the rateof five revolutions per second, giving a flicker rate for each image often per second.

In use, the casing 5' would. be mounted on a suitable support so thatthe range finder could be directed to any desired object field. The instrument would have been calibrated so that the position of the prism [9would indicate the range when the right-hand and left-hand images of thetarget are in coincidence. With the motor 3| running at a suitable rate,coincidence of the targetimages is indicated when the target imageappears not to flicker, that is, when the two images supplement oneanother so as to give the appearance of a. single image of constantbrilliance.

Practically all observers are able=to set the range more accurately withan instrumentusing this flicker feature than with instruments notutilizing flicker. great importance with rapidly moving targets such asairplanes, the increased accuracy of applicants range finder justifiesthe added complieation of providing a rotating shutter.

A modified form of range finder according to this invention comprising aslotted rotating disc shutter is lllustratedin Figs. 4 to 6. .Thismodified range finder-comprises a generally tubular hollow casing 4!!adapted to support the optical elements of a, coincidence range finder.The left-hand image is formed in the focal plane of the ocular M byobjective lens 4-2- utilizing light entering through window 43. Theaxisrot this beam of. light is represented by dot and-dash line H, thedirection of which is changed at right angles four times; first by theoptical square 45, second by the internally reflecting prism ill, thirdby the other internally reflecting face 43 of prism 41, and fourth bythe semi-refleeting face 49 of right triangular prism- 50.. Therighte-hand image is formed also in the focal plane of ocular M byobjective lens ,5! utilizing light entering throughwindow 52. The axisof this beam is represented-by dot-and-dash line. 53-, the direction ofwhich is changed at'right angles also four times; first by theopticalsquare Since accuracy has assumed face 46 of trapezoidal54,.second by the internally reflecting face 55 of trapezoidal prism 56,third by internally reflecting face '51 of prism 56, and fourth by theinternally reflecting face 58 of isosceles triangular prism 59. Thisaxis then pases through the semireflecting face 49 of prism 50. By meansof prism 61] which is movable along the axis 53, as indicated by thedouble-headed arrow 6|, the righthand image formed by objective lens maybe moved transversely in the focal plane of ocular 4|. By means ofadjustable prism 62 in the window 43, the left-hand image formed byobjective lens 42 may be moved both verticall and transversely to effectan infinit setting. The window 52 is closed by a plane glass plate 63.

Apair of slotted disc shutters i4 and 65 are adapted to intermittentlystop the left-hand and right-hand image forming light beams,respectively. Shutters 64 and 65 are secured to the opposite ends of ashaft 66 which is adapted to rotate in bearings of support 61. Securedto the shaft 66 is a spiral gear 68. Gear 68 is rotated by spring-drivenclock-work motor 59 through shaft 10 and spiral pinion II which mesheswith gear 68. Motor 69 is secured toan offset portion 12 of casing 42'The spring of motor 69 is wound by a crank 13 which extends through alighttight opening in the oifset portion 12. A lever 14 which alsoextends from motor 69 through a light-tight opening in offset portion 12is provided for starting and stopping the motor 69. The relative angularposition of the shutters 5t and 65 on the shaft 66 are shown by Figs. 5Aand 5B which are views of the disc shutters looking toward therespective adjacent ends of Fig. f

5. Dotted circles 15 and 16 show the sizes of the left-hand andright-hand image forming beams respectively at the planes of theshutters 64 and 65. As the shutters rotate, each beam is stopped as theother beam is unstopped, the slots and vanes, being of equal sizes. Inorder to produce a flicker rate of about ten cycles per second, adesirable rate as has been pointed out hereinbefore, the shutters withfour vanes will be rotated at the rate of two and one-half revolutionsper second or 150 R. P. M. (revolutions per minute). Casing All in usewould also be suitably mounted so that it could be readily directed tothe object field.

.The operation of the rotating shutter form of flicker range finder isessentially the same as that of the polarized light form. In both formsof range finders the shutters operate to blackout the imagesintermittently and alternately.

The spring-driven, clock-work motor may be used to rotate the sheet ofpolarizing material in the polarized light form of range finder andobviates the necessity for a source of electrical power. An electricmotor also may be used to drive the rotating slotted disc shutters. Theideal locations for the rotating disc shutters are near the objectivelenses 42 and 5|, but such location involves difficulties in mountingand driving these shutters in accurate synchronism. The shutters ma alsobe located in front of the windows 52 and 43. For best results, theshutters should be so arranged that the left-hand image fades out at thesame rate that the righthand image fades in and vice versa, but somedeparture from this ideal condition is permissible without seriouslyaffecting the accuracy of setting the range indicator.

An optical square is a prism of transparent material such as glass soshaped that a beam of light entering one face is twice reflected atinternal faces and emerges in a direction at right angles to thedirection of its entrance. The angle between the reflecting faces is 45degrees. The

optical squares 9, I8, 45 and 54 mentioned hereinbefore are such prisms.Their use in range finders is well known in the prior art.

The optical elements shown diagrammatically in the drawings will, ofcourse, be suitably supported within the casings.

Other modified forms of range finders will be obvious to those skilledin this art from the foregoing description and such modifications comewithin the purview of this invention as defined in the appended claims.

What is claimed is:

1. A range finder comprising means to produce overlapping images of atarget area from separated points of view, means to eliminate saidimages intermittently and alternately at a frequency to produceobservable flicker in each image if viewed by itself, and means toadjust said images transversely relatively to each other wherebycoincidence of the images of a selected target may be effected asindicated by the absence of flicker in such target images.

2. A range finder comprisin two telescopes separated transversely withrespect to their entrance windows and adaptedto be directed toward thesame target area, optical image combining mean whereby images of thetarget area formed by said telescopes may be viewed as overlappingimages, shutter means in the paths of the image forming light rays ofsaid telescopes to eliminate said images from the view of an observerintermittently and alternately at a frequency to produce observableflicker in each image.

3. A range finder comprisin means to produce intermittently andalternately images of the target area from separated points of view inpositions such that said images are overlapping when producedsimultaneously, said images being produced at a frequency to produceobservable flicker in each image if viewed by itself, and means toadjust said images transversely relatively toeach other wherebycoincidence of the images of the selected target may be effected asindicated by the absence of flicker in such target image.

4. A range finder comprisin means to produce two views of an objectfield which are visible to an observer, means to caus said views toappear to coincide at least in part, and means to fade out one of saidviews from and simultaneously fade in the other of said views to theobserver alternately and cyclically at a frequency to produce observableflicker in each view if the other View were continuously obscured.

5. A range finder comprising a light excluding hollow casing having twowindows separated from each other an appreciable distance, an ocularmounted in another opening in said casing, optical means includingobjective lenses individual to each of said windows and beam combiningmeans to form in the focal plane of said ocular overlapping images of anobject field by light entering said windows, means to polarize the lightforming each of said images before the image forming light rays aredirected in a common path, the plane of polarization of the lightforming one image being at right angles to the plane of polarization ofthe light forming the other image in a plane intersecting the commonpath, and an analyzer for polarized light located transversely of thecommon path between the observer's eye and the combining means androtated at a rate to produce observable flicker in the portions of thetwo images which are not in coincidence.

6. A range finder comprising a light excluding hollow casing havin twowindows separated from each other an appreciable distance, an ocularmounted in another opening in said casing, optical means includingobjective lenses individual to each of said windows and beam combiningmeans to form in the focal plane of said ocular overlapping images of anobject field by light entering said windows, sheets of light planepolarizing material intersecting said image forming light beams betweensaid objective lenses respectively and said beam combining means, thepolarizing axes of said sheets being at right angles to each other, ananalyzing sheet of light plane polarizing material intersecting saidcommon path and rotatable in it own plane about an axis perpendicular toits own plane and substantially parallel to the axis of said commonpath, and means to rotate said analyzing sheet at a rate to produceobservable flicker in portions of said two images which are not incoincidence.

'7. A range finder comprising a light excluding hollow casing having twowindows separated from each other an appreciable distance, an ocularmounted in another opening in said casing, optical means includingobjective lenses individual to each of said windows and beam combiningmeans to form in the focal plane of said ocular overlapping images of anobject field by light entering said windows, rotatable disc shuttersmounted between said objective lenses respectively and said beamcombining means to intermittently stop said respective image forminglight beams, one of said beams being stopped while said. other beam isbeing unstopped, and means to rotate said shutters at a rate to causeeach of said images to appear to the observer to flicker.-

8. A range finder comprising a light excluding hollow casing having twowindows separated from each other an appreciable distance, an ocularmounted in another opening in said casing, optical means includingobjective lenses individual to each of said windows and beam combiningmeans to form in the focal plane of said ocular overlapping images of anobject field by light entering said windows, rotatable disc shuttersmounted between said objective lenses respectively and said beamcombining means to intermittently stop said respective image forminglight beams, and means to rotate said shutters to cause one of saidimages to fade out at the same time and rate as the other fades in andvice versa, said rate being such as to make each of said images appearto the observer to flicker.

assume 9. A range finder comprising means to make visible to an observerimages of the same object field from points of view separated by adistance substantially greater than the distance between the pupils ofthe eyes of the observer including means to make the images of aselected object in said object field appear to coincide, and means tofade out one of said images and fade in said other at substantially thesame time and rate and vice versa, the start of a fade out occurring atsubstantially the same instant as the start of a corresponding fade in.

10. A range finder comprising means to make visible to an observerimages of the same object field from points of view separated by adistance substantially greater than the distance between the pupils ofthe eyes of the observer including means to make the images of aselected object in said object field appear to coincide, and meanscomprising polarizing and analyzing elements to fade out one of saidimages and fade in said other at substantially the same time and rateand vice versa, the start of a fade out occurring at substantially thesame instant as the start of a corresponding fade in. c 7

11. A range finder comprising means to make visible to an observerimages of the same object field from points of view separated by adistance substantially greater than the distance between the pupils ofthe eyes of the observer including means to make the images of aselected object in said object field appear to coincide, meanscomprising polarizing and analyzing elements the polarizing axes ofwhich are angularly displaceable relatively to each other, and means todisplace said elements to fade out one of said images and fade in saidother simultaneously at substantially the same rate and vice versa.

12. A range finder comprising means to View images of a target areaproduced from separated points of view and appearing as overlappingimages to the observer, means to fade out one of said images from andsimultaneously fade in another of said images to the view of theobserver alternately and cyclically at a frequency to produce observableflicker in each image if viewed by itself, and means to adjust saidimages relatively to each other to substantially eliminate or noticeablyreduce the flicker of the observed image of a selected target, theposition of the adjusting means indicating the range of the selectedtarget.

HERBERT E. IVES.

